import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.SocketException;

public class UdpEchoServer {
    private DatagramSocket socket = null;

    public UdpEchoServer(int port) throws SocketException {
        socket = new DatagramSocket(port);
    }

    public void start() throws IOException {
        System.out.println("start");
        while (true) {
            //1.接收数据
            DatagramPacket requestPacket = new DatagramPacket(new byte[4096], 4096);
            socket.receive(requestPacket);
            //2.解析并处理数据
            String request = new String(requestPacket.getData(), 0, requestPacket.getLength());
            String response = process(request);
            //3.构造数据报回复
            DatagramPacket responsePacket= new DatagramPacket(response.getBytes(),response.getBytes().length,
                    requestPacket.getSocketAddress());
            socket.send(responsePacket);
            //4.打印日志
            System.out.printf("[%s:%d] req:%s, resp:%s\n",requestPacket.getAddress().toString(),
                requestPacket.getPort(),request,response);
        }

    }

    public String process(String request) {
        return request;
    }

    public static void main(String[] args) throws IOException {
        UdpEchoServer server=new UdpEchoServer(12520);
        server.start();
    }
}

